Mattress



FIG. 1 is a top perspective view of a mattress;

FIG. 2 is a back view of the mattress, the front view being identical thereto;

FIG. 3 is a left side view of the mattress, the right side view being identical thereto; and,

FIG. 4 is a bottom view of the mattress.

The broken lines shown in the drawings are included for illustrating the portions of the mattress, which form no part of the claimed design. 

CLAIM The ornamental design for a mattress, as shown and described. 